1. Field of the Invention
The present invention relates to a multistep bending machine such as a press brake, by which a workpiece can be bent into a relatively complicated shape by continuously bending a workpiece into a plurality of angles of different bending points in multistep bonding process.
2. Description of the Prior Art
In the conventional multistep bending machine, the bending operation is mainly dependent upon the operator's work. In more detail, a backgage (a workpiece end stopper) is located in both horizontal and vertical direction; a foot switch is depressed to bend a located workpiece for the first bending operation; the backgage is again located for the second bending operation before depressing the foot switch again. Therefore, it is necessary for the operator to repeatedly depress the foot switch, thus resulting in a troublesome work and a long bending time.
Further, in the above multistep bending machine, since an already-bent workpiece is repeatedly bent, it is necessary to decide a bending sequence in which no interference of the workpiece with the machine including a pair of bending tools will be produced. In doing this, conventionally, a skilled operator decides the bending sequence on the basis of a finished product (bent into a final shape) and a return bendgraph for each die or on the basis of a number of workpiece drawings describing a bent workpiece shape at each bending process, separately. Therefore, in the case of a complicated bent product, it takes a long time to decide the bending sequence involving no interference with the machine.
Further, when bending speed of a movable tool (e.g. a punch) is too high in relation to a workpiece length from the tool center, the workpiece is excessively bent due to workpiece inertia, thus deteriorating the bending accuracy. Further, when a workpiece is once removed and then inserted into the tool space after turned around in order to prevent the above-mentioned interference, it is necessary to move a movable tool away from a fixed tool. Conventionally, this tool distance is determined by the operator. However, if this distance is too large, this lowers machine efficiency.
Further, it is necessary to locate the workpiece by a backgage stopper member for each bending operation, so that a predetermined bending line is positioned just under the tool. In the case of a flat workpiece, a distance between the stopper member and the tool center can be determined simply. However, in the case of the already-bent workpiece, the distance is not simply calculated according to the shape of the product.
Furthermore, when an already-bent workpiece is located by a backgage stopper member before bending operation and then bent, it is impossible to keep the stopper member as it is, because the extreme end of the workpiece will interface with the stopper member. Therefore, it is necessary to pull-back the stopper member immediately before the bending operation to prevent the interference. Conventionally, this pull-back distance is also determined by the operator.